1. 3.5b DNA structure and replication

2. POINT > Describe the structure of DNA
POINT > Identify the three parts of a nucleotide
POINT > Identify the 4 nucleotides in DNA
POINT > Explain how the structure of DNA makes replication possible

3. DNA: Deoxyribonucleic Acid
Why is DNA so important?
The DNA molecules carry and store the information to build the 1000’s of proteins that cells need to function

4. POINT > Describe the structure of DNA
DNA structure is a double helix

5. POINT > Identify the three parts of a nucleotide
DNA is made of millions of subunits called nucleotides Nucleotides have three parts: 1) a sugar (blue) 2) a nitrogen base -A, G, C, or T (yellow) 3) a phosphate (orange)

6. CHECK:
What are the subunits of DNA called?
What are the three parts of a nucleotide?

7. POINT > Describe the structure of DNA
DNA structure is like a twisted ladder
The rungs of the ladder are held together by hydrogen bonds (weak)
The rungs of the ladder are made of the nitrogen base parts of nucleotides

8. POINT > Describe the structure of DNA
The sides of the ladder are held together by covalent bonds (stronger)
The sides of the ladder are made of the sugar and phosphate parts of nucleotides

9. CHECK: What kind of bond holds the rungs of the DNA ladder together?
What part of the nucleotides makes the rungs of the ladder?
What kind of bond holds the sides of the ladder together?
What part of the nucleotides makes the sides of the ladder?
Which is stronger: hydrogen bond or covalent bond?

10. POINT > Identify the 4 nucleotides in DNA
There are four different nucleotides in DNA
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)

11. POINT > Explain how the structure of DNA makes replication possible
Adenine always hydrogen bonds with thymine (A-T)
Guanine always hydrogen bonds with cytosine (G-C)

12. CHECK:
What is missing?
A : T
T : A G : C
A :
T : A
C :
G : C

13. POINT > Explain how the structure of DNA makes replication possible
Adenine always hydrogen bonds with thymine (A-T)
Guanine always hydrogen bonds with cytosine (G-C)

14. POINT > Explain how the structure of DNA makes replication possible
CHECK: How many nucleotides are in this picture?

15. POINT > Explain how the structure of DNA makes replication possible
During DNA replication the two strands separate
Then other nucleotides fill in, A with T G with C
This creates two new DNA strands

16. POINT > Explain how the structure of DNA makes replication possible

17. POINT > Explain how the structure of DNA makes replication possible
One DNA molecule
Two identical DNA molecules

18. CHECK:
When during the cell cycle does DNA replication happen?
During interphase, in S-phase.
Where does DNA replication happen?
In the nucleus.
Why does DNA replication happen?
So both daughter cells get a copy of the DNA during cell division.

19. Homework:
Read pages
Finish Study Guide
S.A. page 102 #2
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